Super high flow pressure relief vent

Abstract

A pressure relief valve ( 100 ), having: an upper housing ( 104 ) defining a housing internal chamber ( 112 ) and comprising at least one window ( 108 ) between the upper housing chamber and the atmosphere; a lower housing ( 106 ) comprising a housing opening ( 134 ); a pallet ( 170 ) disposed within the housing internal chamber; and a pair of nested springs ( 116 ) disposed within the housing internal chamber and configured to bias the pallet toward the lower housing and thereby form a seal ( 180 ) between the housing opening and the housing internal chamber. When the pressure in the housing opening is at a full discharge pressure that is greater than and within fourteen percent of the start-to-discharge pressure, the pair of nested springs is configured to permit the pallet to travel a sufficient distance to expose a flow area of the at least one window that is at least greater than a flow area ( 138 ) of the housing opening.

The invention claimed is: 
     
       1. A pressure relief valve for a railroad tank car, comprising:
 an upper housing defining a housing internal chamber and comprising at least one window between the housing internal chamber and atmosphere; 
 a lower housing operatively associated with the upper housing and comprising a housing opening; 
 a pallet disposed within the housing internal chamber; and 
 a pair of nested springs disposed within the housing internal chamber and configured to bias the pallet toward the lower housing and thereby form a seal between the housing opening and the housing internal chamber when a pressure in the housing opening is below a start-to-discharge pressure, 
 wherein when the pressure in the housing opening is at a full discharge pressure that is greater than and within fourteen percent of the start-to-discharge pressure, the pair of nested springs is configured to permit the pallet to travel a sufficient distance to expose a flow area of the at least one window that is at least greater than a flow area of the housing opening. 
 
     
     
       2. The pressure relief valve of  claim 1 , wherein the upper housing comprises a cylindrical shape, wherein the pair of nested springs comprises an inner and an outer spring, and wherein the upper housing provides lateral support to an entire length of the outer spring when the pallet forms the seal. 
     
     
       3. The pressure relief valve of  claim 1 , further comprising a cylindrically-shaped alignment device configured to provide lateral support to an inner spring of the pair of nested springs. 
     
     
       4. The pressure relief valve of  claim 2 , wherein the pallet comprises an annular shaped sealing area that forms the seal, and wherein at least one spring of the pair of nested springs rests on an opposite side of the pallet and radially outward of the annular shaped sealing area with respect to an axis of travel of the pallet. 
     
     
       5. The pressure relief valve of  claim 1 , wherein the pallet comprises a sealing area on a sealing side of the pallet, and wherein the pallet comprises no surfaces radially outward of the sealing area that are effective to redirect escaping gases downward and generate a reactive force that acts against the bias of the pair of nested springs. 
     
     
       6. The pressure relief valve of  claim 1 , wherein the pallet comprises a sealing area on a sealing side of the pallet, and wherein with respect to a direction of flow of escaping gases the pallet comprises an upwardly sloped surface disposed radially outward of the sealing area. 
     
     
       7. The pressure relief valve of  claim 1 , wherein the pallet further comprises a receptacle configured to receive a tool, wherein the upper housing comprises a tool aperture, and wherein the receptacle and the tool aperture are configured to receive the tool through the tool aperture and into the receptacle such that the tool can be used to move the pallet against the bias of the pair of nested springs and be supported by the upper housing. 
     
     
       8. The pressure relief valve of  claim 1 , wherein the flow area of the at least one window is at least fifteen (15) percent greater than the flow area of the housing opening. 
     
     
       9. The pressure relief valve of  claim 1 , wherein the pressure relief valve is effective to produce a discharge coefficient of at least 0.92. 
     
     
       10. A pressure relief valve for a railroad tank car, comprising
 a housing defining a housing internal chamber and comprising a wall, at least one window through the wall of the housing and providing fluid communication between the housing internal chamber and the atmosphere, and a housing opening; 
 a pallet; and 
 a biasing arrangement disposed within the housing internal chamber and configured to bias the pallet toward the housing opening and thereby form a seal between the housing opening and the housing internal chamber, 
 wherein when a pressure in the housing opening is at a full discharge pressure that is greater than and within fourteen percent of a start-to-discharge pressure, the biasing arrangement is configured to permit the pallet to travel into the housing internal chamber a sufficient distance to form a vent path between the housing opening and the atmosphere, 
 wherein a lateral portion of a vent path spans from a perimeter of the housing opening to a circumference defined by an outer surface of the housing, and 
 wherein at the full discharge pressure a ratio of a height of the lateral portion of the vent path to a length of the lateral portion of the vent path is at least 0.92:1. 
 
     
     
       11. The pressure relief valve of  claim 10 , wherein the pallet comprises a sealing area on a sealing side of the pallet, and wherein the pallet comprises no surfaces radially outward of the sealing area that are effective to redirect escaping gases and generate a reactive force that acts against the bias of the biasing arrangement. 
     
     
       12. The pressure relief valve of  claim 10 , wherein a sealing side of the pallet comprises a feature that permits vertically upward travel of escaping gases as the escaping gases exit the vent path. 
     
     
       13. The pressure relief valve of  claim 10 , wherein the biasing arrangement comprises a pair of nested springs that exhibit a linear spring constant throughout the travel into the housing internal chamber at least until the vent path is formed. 
     
     
       14. The pressure relief valve of  claim 10 , wherein the housing provides lateral support along an entire length of the biasing arrangement when the pallet forms the seal. 
     
     
       15. The pressure relief valve of  claim 10 , further comprising an alignment device configured to provide lateral support to the biasing arrangement. 
     
     
       16. The pressure relief valve of  claim 15 , wherein the alignment device provides a positive stop to an upper end of a stroke of the pallet. 
     
     
       17. The pressure relief valve of  claim 10 , wherein the vent path is effective to produce a discharge coefficient of at least 0.92. 
     
     
       18. The pressure relief valve of  claim 10 , wherein the lateral portion comprises a lateral portion length that is not greater than twenty five percent of a diameter of the housing opening. 
     
     
       19. The pressure relief valve of  claim 18 , wherein the full discharge pressure the ratio of the height of the lateral portion to the length of the lateral portion is at least 1.06:1. 
     
     
       20. The pressure relief valve of  claim 10 , the vent path comprising a vent path exit having an exit area defined by an arc length of the at least one window multiplied by the height of the lateral portion of the vent path, wherein at the full discharge pressure the exit area is at least fifteen (15) percent greater than a flow area of the housing opening.